Steelers, 49ers square off in a battle of 10-3 teams on Monday Night Football

SAN FRANCISCO — When members of San Francisco's dominant defensive line step into their meeting room, they might start off by discussing life away from football or any personal issue someone is facing. There's usually some clowning around — enough that Ricky Jean Francois has referred to this intense, close-knit group as "Looney Tunes."

The one thing that's never mentioned is an impressive streak that has gone largely unnoticed during San Francisco's remarkable turnaround season: The defense hasn't allowed a single rushing touchdown this year.

If the 49ers (10-3) can keep the AFC power Pittsburgh Steelers (10-3) out of the end zone on the ground Monday night, they will become the first team in NFL history to do so in the first 14 games.

"We take pride in stopping the run," defensive end Justin Smith said. "We don't get into that. I really don't know how many it's been to be honest with you. It's just one of those things, we're in the business of trying to win a football game, not necessarily streaks or stats or anything like that. The main thing is stop the run and give our team a chance to win, and that's what we're all about."

San Francisco also hasn't allowed a 100-yard rusher in 35 straight games — though Pittsburgh's Rashard Mendenhall, with his eight rushing touchdowns, will be determined to try to break one of those streaks.

And Pittsburgh will certainly look to run more if quarterback Ben Roethlisberger doesn't play or is limited because of an ankle injury that forced him to wear a walking boot during the week. He is listed as questionable to play.

"It's not something that's talked about but they do take a lot of pride in it," 49ers coach Jim Harbaugh said. "I think the way our guys, our coaches, our team approach it, is how it plays in to situational football, how it helps us to accomplish the one and only thing we want to accomplish and that's be a winning defense. Win the next game. It's a big factor being able to contain an opponent's running game, to shut down an opponent's running game. To keep them out of the end zone."

One key component in the unit's success has been Jim Tomsula, who led the 49ers to a season-ending victory as interim head coach after Mike Singletary's firing last season before being retained on Harbaugh's staff.

Tomsula regularly wears a true blue-collar shirt with his name stitched into it, fitting perfectly into Harbaugh's approach of being a "blue-collar team" and not a "Hollywood team."

As much fun as Tomsula's group has, these guys are quick to turn it on when the time comes. And they're not above calling each other to task when necessary.

"We'll be in the locker room laughing, and we'll sit over there in practice and laugh and have a cut-up before practice starts," Tomsula said. "And you'll see them, watch their demeanor, it goes from boom to boom. It's just, boom! And I'm not saying the world of D-linemen is a normal place. It's not. And I get all that — it's the Muppets and bouncing off the walls, but it's like, 'Bam! You're on!' If you ever see those kids in kindergarten, some of the kids take the colors and they put nice colors up and they try to draw squares. I think all the guys in my room were the ones with a big mess, a blob of stuff, you know? That's kind of the way it all is, because it's nuts in there! It's crazy! Stuffs flying around and you're like: 'Whoa man! Boom!' That's just the way it is. And they fit, but it's not for everybody."

San Francisco has the top-ranked run D in the NFL, while Pittsburgh owns the No. 1 pass defense.

The Niners are the only team not to allow a rushing touchdown.

"They're playing good solid ball," Mendenhall said. "They're playing together and making plays."

It is often somebody different making big plays depending on the week — from Smith to Patrick Willis, NaVorro Bowman, Ray McDonald or Parys Haralson. That's not even including the defensive backs.

Willis, however, is among several of the marquee players who might be missing for Monday night's matchup.

Roethlisberger is nursing a sprained left ankle and was limited in practice, and he hasn't missed a start because of injury since 2009. Steelers linebacker James Harrison will serve his one-game suspension for a helmet to facemask hit on Browns quarterback Colt McCoy on Dec. 8.

Pittsburgh will play without center Maurkice Pouncey, who had hoped to play despite a sprained left ankle, and wide receiver Emmanuel Sanders (sprained right foot).

Tomlin indicated during the week he might not make a final call on Big Ben's status until before the game at Candlestick Park.

"Of course, a veteran guy like him, he can be ready to play on a limited number of snaps," Tomlin said. "We're always going to be optimistic when it comes to Ben."

Roethlisberger left last Thursday's 14-3 win over Cleveland in the second quarter after spraining his left ankle while getting sacked. He returned to throw for 178 yards and a touchdown in the second half.

"I've been here way too long to count out anybody, let along our center and our quarterback," said Steelers offensive lineman Max Starks. "We'll prepare like they won't be out there, but if they are we'll be more than happy to put them back in the fold. And then let's rock and roll. Ben has been playing with a broken thumb, so nothing would surprise me."

No matter the personnel, Pittsburgh should expect constant pressure from the 49ers.

"I think we've taken another step," Smith said. "We have more steps we can absolutely take. We've put our team in a position to win a lot of games."